Plum Almond Cake

sunflower or vegetable oil, plus more for the pan (I use softened butter)

unbleached all-purpose flour, plus more for the pan (I use 2.5 oz gf flour + 2.5 oz cornmeal)

almond meal or almond flour

baking powder

fine sea salt

large egg

half-and-half or whole milk

Finely grated zest and juice of 1 large lemon

sugar, plus 2 tablespoons (I cut the sugar by half with sweet plums or pluots)

almond extract

to 9 plums (any variety), , halved and pitted but not peeled

sliced almonds

unsalted butter, at room temperature